[LLVMdev] Pool Allocation and DSA (and: Re: DSA Question)

[Torvald Riegel]

On Friday 19 June 2009 18:23:12 Patrick Alexander Simmons wrote:
> Torvald Riegel wrote:
> > On Thursday 11 June 2009 18:14:08 John Criswell wrote:
> >> If your use of pool allocation requires that you can always get the pool
> >> handle for a pointer, you need to make sure that pool allocation is
> >> configured so that it doesn't generate the above scenario.  I think
> >> there is an option to make all pools be global pools.
> >
> > Some time ago, I used AnalysisUsage's
> > addRequired<PoolAllocatePassAllPools>() to get this behavior. It didn't
> > make all pools global.
> >
> > Torvald
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>
> Okay, thanks, Torvald.  I assume this resulted in more pool descriptor
> arguments being passed; did you find this to hurt performance at all?

I needed all of them, so I didn't check whether it hurt performance. It will 
also depend a lot on your target applications. PoolAlloc has some statistics 
for the maximum number of pools per function IIRC.

> Once I have the local pool descriptor, it's occurred to me that what I
> basically need is the interprocedural use-def chain from a pool
> descriptor's Argument to the corresponding Values in the caller
> functions.  Unfortunately, I looked in the class hierarchy and found
> that Argument is not a subclass of User.  Still, perhaps someone has
> created an interprocedural def-use/use-def analysis pass for LLVM for
> some other purpose?

The call sites (call and invoke instrs) are the users of the functions and 
supply the arguments. Several different pool instances might get passed to a 
function. Top-Down and Bottom-Up DSA find these sets to some extend (in order 
to unify the DS nodes and pools), but I think none of them guarantees to find a 
complete unification. I guess looking at Bottom-Up DSA's code should be 
helpful.

Torvald